Hydraulic flow control system and valve with anti-cavitation feature



R. D. KREHBIEL WITH ANTI-CAVITATION FEATURE Filed June 25, 1959 HYDRAULIC FLOW CONTROL SYSTEM AND VALVE April 1s, 1961 sage.

HYDRAULIC FLOW CONTROL SYSTEM AND VALVE WITH ANTI-CAVITA'VIION FEATURE Robert D. Krehbiel, Hutchinson, Kans., assignor to `Cessna Aircraft Company, Wichita, Kans., a corporation of Kansas Filed June 25, i959, Ser. No. 822,858

6 Claims. (Cl. 137-.-622) This invention relates to a system for controlling the ow of uid to and from a double acting hydraulic motor, as Well as to a valve in which the essential components of such system are grouped in a single housing.

The invention is particularly vadapted to control aA double acting cylinder used to raise and lower the boom of a power shovel. Under such conditions of` use, due to the great weight of the boom and its attached bucket, the dropping of the boom from a load dumping position to a digging position causes the plunger in the motor or working cylinder to travel away from the inlet end of the cylinder `at a speed greater than pressure huid can be supplied by the pump to that end of the cylinder, thus causing cavitation, and a consequent delay after the boom is in lowered position before the diggingsoperation can begin.

The present invention eliminates such cavitation and the resulting work delay by supplementing the pump delivery of iiuid to the inlet end of the cylinder with iluid being exhausted under pressure from the outlet end of the cylinder, through a separate iluid transfer circuit or pas- The invention thus insures that an ample quantity of fluid is supplied to the inlet end of the cylinder to keep the cylinder full throughout the dropping of the boom, so that the earth digging operation can begin the instant the boom has reached its proper position.

It is a prime object of the invention to provide a liuid control system and valve which supplements the pump supplied duid owing to the inlet end of the motor'or working cylinder only as and when a supplemental quantity is required to maintain that end of the cylinder com` pletely full, whether the inlet end is the larger volume or smaller volume end of the cylinder. If the volume of uid forced from the exhaust end of the working cylinder exceeds the supplemental quantity required to maintain the inlet endfull, then the excess is delivered into a fluid return passage.

It is an additional object of the invention to provide a system and valve which, when used'to control a boom raising and lowering cylinder or the like, will not only allow the boom tobe dropped freely under its own weight to a digging position, but will speed the downward movement of the boom by supplying uid to the inlet end of the cylinder under full pump pressure and supplemental fluid often under a higher pressure, throughout such downward boom movement.

Another object is to provide -a unitary control valve embodying all the above speciiied features which is well adapted for use with other valves in a multiple valve bank, regardless of the nature and functioning of such other valves.

While my invention is illustrated and described herein for controlling the operation of a boom raising and lowering cylinder, it is well adapted to control a cylinder or motor used for any purpose in which a plunger connected load moves the plunger to exhaust Huid from one end of the cylinder fasterthan the pump is able to supply duid tothe other end thereof. Y Y

Patented Apr. 1S, 1951 Other objects and advantages of the invention will 'be apparent when the following description is read in connection with the accompanying drawing.

The single drawing figure is a longitudinal central sectional view through a unitary control valve embodying my invention, Athe valve being shown schematically installed in a hydr-aulic system which includes a double acting cylinder for vertically actuating the boom of a power shovel.

While the valve shown in the drawing is specifically designed for cooperative association with other valves in a multiple valve bank, and consequently includes a socalled zig-zag type neutral by-pass passage 10 and 11 through which iiuid may continuously flow from the pump discharge back to the reservoir when there is nov demand on the system, it will be understood by those familiar with this art that the invention described herein can be embodied in a valve designed to function independent of any association with other valves in a multiple valve bank. Y

Excepting the control valve shown, the hydraulic system illustrated schematically is considered conventional. A pump 12 is supplied with uid from a reservoir 13 through a conduit 14, and delivers fluid under pressure through a conduit l5, -a relief valve 16, a conduit 17 to a pressure uid passage 1S defined by the valve body 19. Valve body19 has a longitudinal bore 20 which receives a reciprocable valve spool 21, the spool being shown in its neutral position.V

Spool bore 29 is intersected by two communicating fluid pressure ducts 22 and 23 which communicate with the fluid supply passage 18 through a ball check valve 24. Bore 20 is also intersected by two circuit control passages 25 and 26, each located adjacent a respective one of the ducts 22 and 23. The bore is also intersected by the opposite ends of a fluid transfer passage 27, and by the opposite ends of a tluid return passage 23, which openly communicates with a return port 29. The port 29 is connected to reservoir 13 through a conduit 30.

The two circuit-control passages 25 and 26 communicate respectively with motor ports 311 and 32 which are in turn connected by means of conduits 33 and 34 to the opposite ends of a hydraulic motor or double acting cylinder 35.

A pair of conventional settable relief valves 36 and 37 are mounted in the valve body and associated with each of the circuit control passages 25 and 26. These relief Valves are oriented to afford flow of iluid under excessive pressure from either circuit control passage into return passage 2S when the pressure in either circuit control passage rises to a predetermined value above the normal system pressure maintained by the pump-say 200 pounds higher than pump output pressure.

Spool 21 is urged toward its neutral position, shown, by a conventional spring type centering assembly 38. When the spool is in its neutral position it blocks communication between the supply ducts 22 and 23 and thel It also respective circuit control passages 25 and 26. blocks the iiow of fluid from transfer passage 27 to return passage 28.

A settable spring biased ball check valve 39 is housed in spool 21, and communicates with ports 4t) and 41 in the spool to aord iiow of iluid from transfer passage 27 into return passage 28 when the pressure differential between the two is greater than the setting of the valve 39.

Near its other end spool 21 houses a simple conventional check valve 42, the ball being normally held on its seat by the higher pressure in circuit control passage 26.

Throughv ports 43 and 44 check `valve 42 aiods aY flow t of lluid from the fluid transfer'passage 27 into circuitI assunse Operation When the boom Sis in the raised position shown in the drawing and the operator desires to lower or drop it, he moves spool 2l to the left. This movement connects supply duct 2? with circuit control passage 26, and connects Icircuit control passage with fluid transfer passage 27. l-ressure fluid flows from supply passage 1'8 through duct 23, circuit control passage 26 and line 34 to the inlet end of working cylinder 35. Due to gravity, boom 45 begins to drop toward a lowered position the instant spool 21 is shifted to the left. Such boom movement causes plunger 46 to move outward away from the inlet end of the cylinder. As the boom drops it causes the plunger to force fluid from the exhaust end of the cylinder through line 33, circuit control passage 25, and into transfer passage 27.

If the downward velocity of the dropping boom causes the plunger 55 to force fluid out of the cylinder faster than pump l2 can `supply pressure fluid to the inlet end of the cylinder, the pressure in fluid transfer passage 27 rises to a value greater than the pressure in circuit control passage ti. Fluid thus flows from the transfer passage through port fici, check valve 42., and port 43 into the circuit control passage 26 to supplement the fluid being pumped through that passage to the inlet end of the cylinder. The inlet end of the cylinder is thus supplied iluid as fast as fluid is being forced from the other end of the cylinder by the plunger.

'As soon as the pressure in circuit control passage 26 again rises to a value greater than that required to open check valve 39, the excess fluid being returned from the cylinder 46 flows through valve 39 into return passage 2?: and back to the reservoir thro-ugh return port Z9 and line 3f?.

When it is desired to raise the boom from a digging position to the position shown in the drawing, the operator moves the flow control spool 2l to the right of its neutral position. This movement connects fluid pressure duct 22 with circuit control passage 25 and fluid flows through line 33 to` the outer end of cylinder 35 and forces the plunger i6 inward. Fluid is thus forced from the inner end of the cylinder through line 34, circuit control passage 26 directly into the adjacent end of fluid transfer passage 27. It then flows from fluid transfer passage 27 freely into return passage 28 and to the reservoir.

lt will be understood that the spring biased check valve 39 opens only in response to a pressure differential which is greater than that required to open the check valve 42. Thus the flow of fluid from the transfer passage 27 flows into circuit control passage 26 when there is a demand for additional fluid in that passage, and when there is no such demand the fluid flows from transfer passage 2'7 through valve 39 and into the return passage 28.

From the above description it will be seen that my invention provides a means for preventing cavitation in one end of a cylinder when the plunger in the cylinder is forcing fluid out of the other end of the cylinder faster than the pump can supply fluid to the inlet end of the cylinder, and that such means generally comprises: fluid supply, fluid transfer and fluid return passages; two separate circuit control passages connected respectively to the opposite ends of the motor and connectible to the` fluid supplyv and fluid transfer passages; shiftable'valve means efective'in a neutral position to block the flow of supply 4 a fluid into either circuit control passage and to block the flow of return fluid from either circuit control passage into the transfer passage, and shiftable to selectively connect either circuit control passage with the supply passage while directly connecting the other circuit control passage with the transfer passage; independent valve means which affords flow of fluid from the transfer passage into a rst of said circuit control passages when the pressure therein drops below the pressure in the transfer passage, and when the shiftable valve means is in a position to connect said rst circuit control passage with the supply passage, and to connect the second circuit control passage with the transfer passage; and independent valve means openable in response to a pressure differential greater than that required to open the last above mentioned valve means to afford flow of fluid from the transfer passageinto the return passage when the shiftable valve means is in the last above specified position.

Having described the invention with sufficient clarity to enable those familiar with this art to construct and use it, l claim:

1. A system for controlling the operation of a fluid actuated motor and for preventing cavitation therein when large load inertia forces are transmitted thereto, said system comprising: fluid supply, fluid transfer and fluid return passages; two circuit control passages connected respectively to the opposite ends of the motor and selectively connectible to the fluid supply and fluid transfer passages; shiftable valve means including spaced land portions and adjacent grooves, certain of said land portions being effective in a neutral position to block the flow of supply fluid to and from both circuit control passages, the shiftable valve means being movable to positions in which said grooves selectively connect either circuit control passage with the supply passage while directly connecting the other circuit control passage with the transfer passage; first independent valve means affording flow of fluid from the transfer passage into a first of said circuit control passages when the pressure therein drops below the pressure in the transfer passage and when the shiftable valve means is in a position to connect said first circuit control passage with the supply passage and the second circuit control passage with the transfer passage; and second independent valve means openable in response to a pressure differential greater than that required to open the last above mentioned valve means to afford flow of fluid from said transfer passage into said return passage when the shiftable valve means is in the last above designated position.

2. The fluid flow control system described in claim 1, and two pressure relief valves, one associated with each circuit control passage, each relief valve being oriented and located toy afford flow of fluid from its respective circuit control passage directly into said return passage.

3. A system for controlling the operation of a fluid actuated motor and for preventing cavitation therein when large load inertia forces are transmitted thereto, said system comprising: fluid supply, fluid transfer and fluid return passages; two circuit control passages connected respectively to the opposite ends of the motor and selectively connectible to the fluid supply and fluid transfer passages; shiftable valve means including spaced land portions and adjacent grooves, certain of said land portions being effective in a neutral position to block the flow of supply fluid to and from both circuit control passages, the shiftable valvel means being movable to positions in which said grooves selectively connect either circuit control passage with the supply passage while directly connecting the other circuit control passage with the transfer passage; a spring biased check valve oriented and located with respect to said shiftable valve means to afford flow of fluid from one circuit control passage through the transfer passage into the return passage only when the shiftable valve means is in a position to connect the supply passage with the otherv circuit controlV passage; and a differential pressure opened check valve oriented and located with respect to said shiftable valve means to afford flow of fluid from the transfer passage into said other circuit control passage only when said shiftable valve means is in a position to connect the supply passage with said other circuit control passage, and only when the fluid pressure in said transfer passage exceeds the pressure in said other circuit control passage, said differential pressure opened valve being openable by a differential pressure less than that required to open said spring biased check valve.

4. A valve for controlling the operation of a fluid actuated motor and for preventing cavitation therein when large load inertia forces are transmitted thereto, said valve comprising: a housing having a bore therein; pressure fluid supply, fluid transfer and fluid return passages defined by the housing, all communicating with said bore; two circuit control passages defined by the housing, both communicating with said bore and in open communication with the opposite ends of the motor to be controlled; shiftable valve means in said bore, said valve means including spaced land portions and adjacent grooves, certain of said land portions being effective in a neutral position to block flow of fluid from the supply passage to the circuit control passages, and from the circuit control passages into the transfer and return passages, said shiftable valve means being movable to motor operating positions in which certain of said grooves selectively afford flow of pressure fluid from the supply passage into either circuit control passage and thence to the motor, While simultaneously affording flow of return fluid from the motor through the other circuit control passage into the transfer passage; a spring biased check valve oriented and located with respect to said shiftable valve means to afford ilow of fluid from the transfer passage into the return passage only when the shiftable valve means is in one motor operating position; and a differential pressure opened check Valve oriented and located with respect to said shiftable valve means to aord flow of fluid from the transfer passage into one circuit control passage only when the shiftable valve means is in the said one motor operating position, and only when the pressure in the transfer passage exceeds the pressure in said one circuit control passage, said differential pressure opened valve being openable by a differential pressure less than that required to open said spring biased check valve.

5. A valve for controlling the operation of a fluid acuated motor and for preventing cavitation therein when large load inertia forces are transmitted thereto, said valve comrising: a housing having a bore therein; pressure fluid supply, fluid transfer and fluid return passages defined by the housing, all communicating with said bore; two circuit control passages defined by the housing, both communicating with said bore and in open communication with the opposite ends of the motor to be controlled; shiftable valve means in said bore, said valve means including spaced land portions and adjacent grooves, certain of said land portions being effective in a neutral position to block flow of fluid from the supply passage into the circuit control passages, and from the circuit control passages into the transfer and return passages, said shiftable valve means being movable to positions in which said grooves and land portions cooperate to selectively connect and block the passages as follows: to connect the supply passage with a first circuit control passage and the communicating rst end of the motor while connecting the second circuit control passage and the second end of the motor to the transfer passage, and while also connecting the transfer passage with the return passage; to connect the supply passage with the second circuit control passage and the second end of the motor while connecting the first circuit control passage and first end of the motor with the transfer passage and while also blocking flow from the transfer passage into the 'return passage; a spring biased check valve oriented and located with respect to said shiftable valve means to afford flow of fluid from the transfer passage into the return passage only when the shiftable valve means is in a position in which a land portion thereof is blocking flow from the transfer passage into the return passage; and a differential pressure opened check valve oriented and located with respect to said shiftable valve means to afford flow of fluid from the transfer passage into said second circuit control passage when the first circuit control passage is connected to the transfer passage and when the pressure in the transfer passage exceeds the pressure in said second circuit control passage, said differential pressure opened valve being openable by a differential pressure less than that required to open said spring biased check valve.

6. In a unitary control valve assembly, an elongated housing having a longitudinal bore therein, first and second longitudinally spaced transversely disposed circuit control passages intersecting said bore and extending outwardly therefrom and adapted to be connected to the opposite ends of a fluid motor, a supply passage intermediate the first and second circuit control passages and eX- tended into said bore and adapted to be connected to a source of pressure fluid, a generally longitudinally disposed transfer passage having its opposite ends extended into said bore, a generally longitudinally disposed return passage lying outwardly of the transfer passage and having its opposite ends respectively spaced longitudinally of the opposite ends of the transfer passage and extended into said bore, a shiftable spool valve slidably received in the bore, said spool valve including recessed end portions and a plurality of cylindrical land portions, certain of the land portions being effective when the spool valve is in a neutral position to block flow of fluid from the supply passage into the first and second circuit control passages and from said first and second circuit control passages into the transfer and return passages, said certain land portions also being effective to selectively connect either of the first and second circuit control passages with the supply passage while another of said land portions directly connects the other of the first and second circuit control passages with the transfer passage, a first pair of ports in the spool valve interconnecting one recessed end portion thereof with the transfer passage and said first circuit control passage, a ball check valve interposed between said first pair of ports in said one recessed end portion of the spool valve, said ball check valve permitting flow of fluid from the transfer passage into said first circuit control passage when said spool valve is in a position to connect the supply passage with said first circuit control passage and when the fluid pressure in the transfer passage exceeds the pressure in the first circuit control passage, a second pair of ports in the spool valve interconnecting the other recessed end portion thereof with the transfer and return passages, a spring biased check valve interposed between said second pair of ports in said other recessed end portion of the spool valve, said spring biased check valve permitting flow of fluid from the second circuit control passage through the transfer passage into the return passage when said spool valve is in a position to connect the supply passage with the first circuit control passage and when the pressure is in excess of that required to open said ball check Valve.

References Cited in thefile of this patent UNITED STATES PATENTS 2,267,284 rivers Dec'. 23, 1941 2,367,682 Kehle Jan. 23, 1945 2,646,025 Deardorff July 2l, 1953 

